1. Field of the Invention
This invention relates to orthodontic treatment systems wherein resilient appliances are used in sequence to move the patient's teeth to desired orientations in the dental arch.
2. Description of the Related Art
Orthodontic treatment involves movement of malpositioned teeth to improved orientations. Orthodontic treatment can greatly enhance the aesthetic appearance of the patient's teeth, especially in regions near the front of the oral cavity. Orthodontic treatment can also improve the patient's occlusion so that the teeth function better with each other during mastication.
One type of orthodontic treatment is carried out by the use of elastomeric positioning appliances, also known as repositioning trays or alignment trays. These appliances have overall, generally “U”-shaped configuration that generally matches the shape of the patient's dental arch, and a row of receptacles in the appliance receive respective teeth of the dental arch. Some patients favor elastomeric positioning appliances because they can be removed while eating.
Elastomeric positioning appliances are often made by first taking an impression of the patient's dental arches and then making a plaster of Paris or “stone” model from the impression. Next, the teeth of the stone model representing the teeth to be moved during treatment are cut or sawn from remaining portions of the model and repositioned as desired, using a wax or other material to hold the repositioned teeth in place. A sheet of thermoplastic material is then placed over the model and heated such that the sheet is formed into the exact shape of the model with the repositioned teeth. Subsequently, edges of the sheet are trimmed as desired to form a tray. When the tray is set in place over the patient's dental arch, the elastic characteristics of the thermoplastic material tend to move the teeth toward the orientations as represented by the repositioned teeth of the model.
A system of elastomeric positioning appliances available from Align Technology, Inc. of Santa Clara, Calif. involves a series of alignment trays that are used in sequence. The trays are custom-made for each patient, and each tray is constructed to move the teeth along an incremental portion of the treatment path. One possible method of making such positioning trays is somewhat similar to the method described above, except that a model is provided for each tray of the series and the teeth are repositioned on each model in accordance with the intended incremental positions of the patient's teeth along the desired treatment path.
Another type of orthodontic treatment is carried out by the use of a series of tiny, slotted brackets, each of which is affixed to a respective tooth of the patient's dental arch. A resilient arch member such as a curved, elongated archwire is placed in the slot of each bracket. Ends of the archwire are often received in devices known as buccal tubes that are affixed to the patient's molar teeth. The archwire serves as a track to guide movement of the teeth to desired positions.